initial commit

src/common/dto/normalized-error.dto.ts

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+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+
+/**
+ * Standardized error shape returned to API consumers
+ * regardless of upstream provider error formats.
+ */
+export class NormalizedErrorDto {
+  @ApiProperty({ example: 'PROVIDER_TIMEOUT' })
+  code!: string;
+
+  @ApiProperty({ example: 'Provider request timed out' })
+  message!: string;
+
+  @ApiPropertyOptional({ example: 'سرویس در دسترس نیست' })
+  providerMessage?: string;
+
+  @ApiPropertyOptional({ example: '503' })
+  providerCode?: string;
+}